This invention relates to automatic welding equipment and more particularly to a multihead welding gun, which simultaneously produces a plurality of seal welds at the juncture of a plurality of tubes with the tube sheet.
In heat exchangers such as nuclear steam generators, wherein it is necessary to ensure a leakless joint between the tubes and the tube sheets, rolling or expansion of the tubes into the tube sheet does not provide assurance of a leakproof juncture so that the tubes are generally seal welded to the tube sheet. To improve the uniformity of the welds and control the penetration, the molten puddle solidification and the bead sag, automatic welding has been utilized, however, the weld guns hereinbefore utilized could only make one weld at a time. To make multiple welds is a problem as the ligaments between tubes varies to a degree that multi-fixed head guns would not produce acceptable welds, each weld head must be axially aligned with the tube to be welded within a tolerance, which is much smaller than the economical tolerance of the pitch of holes in a tube sheet.